Biodiesel produced from renewable sources like vegetable oils and animal fat is an attractive alternative fuel (Krawczyk 1996). In biodiesel production using transesterification of triglycerides, glycerol is the major byproduct produced; about 1 kg of glycerol is formed for every 9 kg of biodiesel produced (Dasari et al. 2005). Biodiesel consumption in the United States has increased dramatically from 75 million gallons in 2005 to 700 million gallons in 2008. The latter resulted in the production of around 50 million gallons of glycerol (http://biodiesel.orgiresources/faqs/, (Dasari 2007)). Refined glycerol has numerous applications in food, drug, textile and cosmetic industries whereas crude glycerol produced from biodiesel industry is of low value because of its impurities like spent catalyst, salts after neutralization, residual methanol, methyl esters and free fatty acids (Liu et al. 2002; Boumay et al. 2005). The economies of biodiesel industry is strongly influenced by the value of its byproducts. Developing new uses of biodiesel glycerol is imperative to economics and sustainability of the biodiesel industry (Demirbas 2003; Haas et al. 2006).
Arabitol is a polyhydric alcohol that can be used as a low calorie sweetener (Huck et al. 2004). In addition, a study by the Department of Energy identified arabitol, and its enantiomer xylitol, as ode of the top twelve biomass-derivable building block chemicals. Arabitol and xylitol can be transformed into several groups of chemicals like xylaric/xylonic acid, arabonic/arabinoic acid, propylene glycol and ethylene glycol (Werpy and Petersen 2004). Arabitol and xylitol have melting points of 103° C. and 93° C., respectively. Both are highly soluble in water and both form white crystals when purified (Le Toumeau 1966; Talja and Roos 2001). The catabolism of arabitol by Escherichia coli involves the formation of arabitol phosphate which induces the synthesis of compounds that inhibit the bacterial metabolism (Scangos and Reiner 1979). While more studies are required, the above property makes it possible to use arabitol as sweetener for reducing dental canes. Also, the caloric value of arabitol is 0.2 kcal/g whereas it is 2.4 kcal/g for xylitol, it is highly possible that arabitol can be used in many of the known applications of xylitol, as a natural sweetener, a dental caries reducer and a sugar substitute for diabetic patients (Gare 2003). If desirable, arabitol can also be converted to xylitol, for example, by using Glucanobacter oxydans (Suzuki et al. 2002). This bacterium was capable of oxidizing D-arabitol to D-xylulose using the membrane-bound D-arabitol dehydrogenase and then converting D-xylulose to D-xylitol using the also membrane-bound D-xylitol dehydrogenase. Xylitol yield of around 25% has been reported (Sugiyama et al. 2003).
Xylitol is currently produced in one embodiment by chemical reduction of xylose derived from wood hydrolysate under alkaline conditions (Melaja and Hamalainen 1977). This process requires high pressure (50 atm) and temperature (80-140° C.) and uses relatively expensive catalyst and relatively extensive separation steps. Xylitol production from xylose by biological processes has also been explored (Leathers et al. 2000; Kim et al. 2002; Kastner et al, 2003; Buhner and Agblevor 2004). Yeast can covert xylose to xylitol using NAD(P)H-coupled xylose reductase. Unfortunately, the xylitol produced tends to be oxidized to xylulose by NAD+-coupled xylitol dehydrogenase. Good xylitol yields from such a process require tightly controlled, high intracellular NAD(P)H/NAD+ ratios. This control is not an easy task in large-scale industrial operations where the environment (particularly the dissolved oxygen concentrations) inside the large bioreactors is not homogeneous. The above chemical and biological processes require costly separation of xylose from the complex sugar mixtures in the biomass hydrolysate. The alternative approach of producing arabitol from biodiesel glycerol and then, if desirable, converting arabitol to xylitol may prove economically attractive. Arabitol is known to be produced by osmophilic yeast species such as Debaryomyces Candida (Bernard et al. 1981), Pichia (Bisping et al. 1996), Hansenula (Van Eck et al. 1989) and Endomycopsis (Hajny 1964). When exposed to osmotic stress, the yeast accumulates compatible solutes such as arabitol, glycerol, xylitol, erythritol and mannitol to balance the osmotic pressure across the cell membrane.
U.S. Pat. No. 2,793,981 relates to the production of polyhydric alcohols. More particularly it relates to the simultaneous formation of glycerol and D-arabitol by fermentation of a sugar.
U.S. Pat. No. 2,934,474 relates to the production of polyhydric alcohols, and in particular to the production of D-arabitol, by fermentation.
U.S. Pat. No. 3,607,652 relates to a process for the fermentative production of D-arabitol by cultivating under aerobic condition a micro-organism Pichia ohmeri No. 230 (ATCC Deposit No. 20209) in a nutrient medium containing fermentable saccharides such as glucose, sucrose, mannose, fructose and the like as carbon source, and recovering D-arabitol accumulated in the cultivated liquor. D-arabitol is reportedly obtained at a high yield without substantial formation of other polyhydric alcohols having similar properties.
U.S. Pat. No. 4,271,268 relates to the preparation of D-arabitol by a fermentative process utilizing a micro-organism of the species Pichia haplophila or mutants thereof in a nutrient medium containing as a carbon source a hydrocarbon or ethyl alcohol.
U.S. Pat. No. 5,846,794 relates to a process for the preparation of D-arabitol, characterised in that it comprises the following stages: hydrolysis of a lactose solution, oxidation of the mixture of glucose and galactose thus obtained to a mixture of gluconic and galactonic acids, decarboxylation of this mixture of gluconic and galactonic acids to a mixture of D-arabinose and D-lyxose, catalytic hydrogenation of this mixture of D-arabinose and D-lyxose to D-arabitol.
Production of D-arabitol by a Newly Isolated Kodamsea ohmeri, in Bioprocess Biosyst Eng (2010) 33:565-571, reports production of arabitol from glucose using a specific strain. The work was done in shake flasks without pH and DO (dissolved oxygen concentration) control. The species produces glycerol and ethanol as the byproducts, with 8 and 20 g/L concentration respectively.
In view of the above, it would be desirable to provide a method for the production of arabitol, using biological fermentation agents and processes.